The recycling of urea to the rumen was studied in Merino ewes during different physiological states using radioactive tracers. The results showed that although the proportion of urea recycled differed, similar amounts were recycled in dry and pregnant sheep over a wide range of N intake. Urea recycling increased significantly during lactation on all diets when compared with non-lactating sheep. Thus, factors other than simple diffusion of urea control urea recycling in sheep although the control mechanisms remain undefined.